Data storage devices such as disk drives are used for data storage and retrieval in a variety of applications. A disk drive includes a disk for storing information, a transducer (read/write) head for reading data from and writing data to the disk, a spindle motor for rotating the disk, a head carrier that supports the transducer head and an actuator for moving the head carrier and the transducer head. The disk drive may include multiple disks separated by spacer rings and stacked on a hub attached to the spindle motor, multiple transducer heads and multiple head carriers that each support at least one transducer head. The disk includes concentric tracks that each include servo sectors and interleaved data sectors. To access a data sector, the transducer head is moved radially across the tracks in a seek operation to the destination track that contains the data sector, and then the disk rotates the data sector under the transducer head for reading data from or writing data to the data sector.
The disk drive further includes a preamplifier connected to the transducer head. The preamplifier provides two mutually exclusive data transfer modes: a read mode in which data recorded on the disk is sensed by the transducer head and transmitted to the preamplifier for amplification in a read operation, and a write mode in which data transmitted to the preamplifier is recorded on the disk by the transducer head in a write operation.
The disk drive has timing constraints which limit performance due to the read and write operations being mutually exclusive (not overlapping or simultaneous). For example, the disk drive cannot (1) self-servo write by reading a reference pattern from one disk surface while writing servo patterns to another disk surface, (2) reprocess (erase) a previously written disk by reading from one disk surface while writing an erase pattern to another disk surface without an external positioning device or a time consuming algorithm, (3) reduce test time by reading from one disk surface while writing to another disk surface, (4) increase read accuracy by reading head position information from one disk surface while writing to another disk surface, or (5) increase write accuracy by reading from one disk surface while writing to another disk surface.
The servo patterns in the servo sectors provide head position information to enable the actuator to move the transducer head from the starting track to the destination track during a seek (track-to-track) operation, and to maintain the transducer head in proper alignment with the track centerline of the destination track while data is read from or written to the destination track during a track-following (on-track) operation. The servo patterns typically have uniform angular spacing and include circumferentially sequential, radially staggered single or multiple frequency bursts.
The servo patterns can be written using a servo writer. The servo writer is a complex and expensive machine typically stabilized on a large granite base to minimize unwanted vibration and employs laser interferometry for precise position measurements. The servo writer typically requires direct mechanical access to the head carrier and includes a fixed head for writing a clock track on a disk surface. The servo writer writes the servo patterns before the disk drive is sealed against particulate contamination.
The servo writer is typically located within a clean room where the air is purged of impurities that might otherwise interfere with the servo writing or normal disk drive operation after manufacturing. Further, servo writing by the servo writer is very time consuming. In one example, a disk drive having two disks with four disk surfaces can require three servo writer controlled passes of the transducer head over a single track, consuming a total servo writing time as long as 18.2 minutes. Servo writing using servo writers in clean rooms requires both considerable capital investment and severe time penalties attributable to servo writer bottlenecks. Further, as track densities increase with evolving disk drive designs, servo writers have to be replaced or upgraded at considerable capital expense.
The servo patterns can also be written using self-servo writing. A reference pattern at full resolution is magnetically printed on a disk surface of a reference disk by a magnetic printing station during a pre-assembly operation. The reference disk with the reference pattern is then assembled with blank disks into the disk drive. After the disk drive is sealed, the disk drive uses the reference pattern to self-servo write embedded servo patterns on each disk surface within the disk drive. Thereafter, the reference pattern is erased, leaving the disk drive with properly located servo patterns on every disk surface, including the disk surface which included the reference pattern. However, disadvantages of this approach include (1) the self-servo write is time consuming, (2) repeatable run-out must be removed during the self-servo write, (3) the magnetic printing station is expensive, and (4) the reference disk has no absolute reference and since read and write operations are mutually exclusive, defects in the reference disk can exacerbate the problem.
There is, therefore, a need for a data storage device, such as a disk drive, with simultaneous read and write capability. There is also a need for self-servo write with simultaneous read and write operations to cost effectively enhance data storage device manufacturing and performance.